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Engine Building Fundamentals: Engine Block

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Engine Block


00:00 - Let's start our analysis of engine components with the engine block, which is also referred to as the bottom end of the engine.
00:08 This is an area of the engine that's going to see a lot of focus from us during this course, and there's a lot of work required here, both in regards to the machining work, as well as the measuring and assembly work.
00:20 The actual cylinder block in the majority of modern production engines will be cast from aluminium, which offers a reduction in weight, in comparison to the more traditional cast iron that was common until recently.
00:34 If we start at the top of the block, we have the deck surface, which is where the cylinder head mates to.
00:41 The finish of the deck surface is critical, as this will have a large impact on the ability of the head gasket to adequately seal the block to the cylinder head.
00:51 Of course, the block will also be drilled and tapped for the bolts used to fasten the cylinder head to the block.
00:58 In the centre of the block, we have the bores, which are where the pistons are going to run.
01:04 You'll find that, when it comes to engine terminology, there're often several names to refer to the same part, and the bores are also often referred to as cylinders.
01:15 The size and finish of the engine block's cylinders is one of the most critical aspects of engine machining, as this will effect the clearance between the piston and the cylinder wall, as well as how well the piston rings will seal.
01:30 In particular, though, we want to achieve a cylinder that is perfectly round, as well as perfectly parallel from the top to the bottom.
01:40 This might sound obvious, and maybe it should go without saying, but perhaps, surprisingly, it's actually quite difficult to achieve these aims with the sort of precision we need.
01:52 We also want to ensure that each cylinder is machined in the correct orientation to its corresponding crankshaft journal, and that it's machined perpendicular to the plane of the crankshaft, and that all of the cylinders are parallel to each other.
02:06 Around the outside of each cylinder is a water jacket where the engine coolant flows.
02:14 This allows the coolant to remove the heat from the engine, and transfer it to airflow by means of the radiator.
02:21 By and large, the combustion process is incredibly wasteful, and the majority of energy that comes from the combustion process is wasted in the forms of heat and sound.
02:33 The task of the cooling system is to manage the heat.
02:36 Since the majority of the heat produced by the engine occurs in and around the combustion chamber, the coolant also needs to pass up through ports in the head gasket, and into the cylinder head to continue its job there.
02:52 This is why we will see ports in the deck surface of the block that access into the coolant jacket.
02:58 How these ports look will depend a little on the material the block is manufactured from, as well as the actual manufacturing process.
03:09 With a cast-iron block, we're typically going to have what's known as a closed deck block, where the deck surface is primarily solid with relatively small slots, or holes, for this fluid to bypass.
03:23 In aluminium blocks, on the other hand, it's quite common to have what's known as an open deck block, where the cylinders are almost completely detached from the outside of the cylinder block.
03:34 This makes the casting process simpler.
03:37 However, open deck blocks can suffer from head gasket sealing issues at high power levels as the cylinders themselves can distort and move around under high cylinder pressure, since they aren't stabilised by the rest of the cylinder block, as would be the case in a closed deck block.
03:57 In cast iron blocks, the piston rings can run directly on the cast iron material, once it's been correctly finished.
04:04 However, with aluminium blocks, there's a little more involved, since the raw aluminium material would quickly be worn away by the rings.
04:14 For this reason, an aluminium block will usually have an iron sleeve or liner in each cylinder, which the piston rings run on.
04:23 An alternative to cylinder liners or sleeves that's also used in some applications is a nickel-seal coating that's applied directly to the aluminium cylinder surface.
04:33 Lastly, while we're still considering the deck surface of the block, we'll also have a high pressure oil gallery that's used to supply oil up into the cylinder head, as well as some drains that're used to return the oil back into the sump.
04:49 Now, we'll move down to the crankshaft journals in the block, which is where the crankshaft is supported.
04:56 The crankshaft journals are an integral part of the cast block, and in most cases, there will be a journal at the front and the rear of the engine block, as well as a journal between each cylinder, or pair of cylinders in the case of a V configuration engine.
05:11 Each journal also includes a cap that can be bolted to the engine block once the crankshaft is physically installed.
05:19 While individual caps for each journal on the crankshaft are common, on high performance engines, it's quite common for all of the main bearing caps to be supported and connected with what's known as a girdle, or a cradle.
05:33 This helps stabilise the main bearing caps, and prevents them moving under very high loads.
05:40 A common upgrade with engines that only offer individual caps is to fit an aftermarket cradle to tie all of the caps together, or in some instances, even tie them to the sump rails of the block as well.
05:54 An alternative, where individual caps with only two bolts are fitted, is to fit an aftermarket cap that's supported by either four or six bolts to improve the way the cap is located and fastened to the engine block.
06:11 The crankshaft is supported in the engine block by a set of bearings and a steady supply of high pressure oil is essential to the life of these bearings, as well as the crankshaft.
06:24 The main bearings are normally fed oil directly from the main oil gallery that will usually run through the block from the front to the rear, before connecting to the oil gallery feeding the cylinder head.
06:36 This oil supply to the main bearings also supplies oil to the internal oil galleries in the crankshaft, which in turn supplies oil to the conrod bearings.
06:49 A critical measurement relating to engine blocks is known as the deck height, which refers to the distance from the centre line of the crankshaft journal to the deck surface of the block.
07:02 This is critical because the deck height, combined with a crankshaft stroke, conrod length, and compression height of the piston will define where the piston sits, relative to the deck of the block when it's at TDC.
07:16 This has large implications on both the compression ratio of the engine, as we'll see later, as well as more critical aspects such as piston to head clearance, and piston to valve clearances.
07:29 At the rear of the engine block, we'll have a crankshaft seal that's referred to as the rear main, or rear main seal.
07:36 This seal is typically a cast housing that supports a rubber seal, which will run directly against a machined surface on the crankshaft.
07:46 At the front of the engine, we'll also have a cover assembly that seals the engine and the crankshaft.
07:53 This is referred to as the front cover.
07:55 As with the rear main seal, the front cover will incorporate a seal that runs against the crankshaft to seal the engine, and prevent oil leakage.
08:06 In some instances, the front cover will also incorporate the oil pump, and this may be either directly driven off the crankshaft, or it may be gear driven, as part of the cam drive mechanism.
08:19 In other instances, the oil pump assembly may be an entirely separate item that's installed prior to assembling the front cover of the engine.
08:30 The engine block, in some cases, will also be home to a balance shaft or balance shafts, which are used to counter the natural harmonics that occur during engine operation.
08:43 These are commonly found in in-line three and four cylinder engines, as well as V6 engines, since their design results in an inherent imbalance that can't be eliminated simply by balancing the engine components.
08:58 To reduce vibration and harshness, many manufacturers have chosen to fit balance shafts.
09:05 It's common, although not essential, when modifying some engines for performance or competition use to eliminate the factory fited balance shafts.
09:14 This can free up a small amount of engine power, and it also removes a potential failure point, reducing the engine complexity.
09:25 In pushrod applications, where the valves are actuated by pushrods, rather than directly by the camshaft, the block will also be home to the camshaft.
09:35 The camshaft will be located in its own set of journals and bearings, either above the crankshaft in V configuration engines, or offset to the side in inline configuration engines.
09:48 As well as the camshaft, pushrod engines will also have machined bores for the lifters to run into.
09:55 Next, we have the sump that bolts to the block, and acts as an oil reservoir.
10:01 There'll also be a pickup that attaches to the oil pump assembly, and protrudes down into the bottom of the sump to ensure a constant supply of oil is always available to the oil pump.
10:14 The lower rails of the engine block where the sump bolts to are often referred to as the sump rails.
10:21 Finally, on the outside of the block, we'll have a location for an oil filter, which is essential to remove dirt and debris from the engine oil.